2013 Workflow Task Failure

I am having a recurring, repeatable problem with SharePoint Online.  Any 2013 workflow I create with a task assigned will fail with this error:

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Here is a real workflow this problem occurs on:

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Here are the troubleshooting steps I've tried:

1. Deleted the workflow and recreated it.
2. Deleted the list and recreated it.
3. Deleted the task list and recreated it.
4. Deleted all three and recreated them.
5. Deleted the entire site collection, removed from recycle bin and recreated it.

Note that if I create an equivalent workflow using 2010 Workflows, it works as expected.

Thanks,

DS